1. Field of the Invention
The present invention relates generally to subterranean well completion, servicing, and rework and more particularly to an autonomous system for operating a well tool in a wellbore for purposes of completion, servicing, and rework.
2. Description of the Related Art
In the drilling and completion of oil and gas wells, a wellbore is drilled into a subsurface producing formation. Typically, a string of casing pipe is then cemented into the wellbore. An additional string of pipe, commonly known as production tubing, may be disposed within the casing string and is used to conduct production fluids out of the wellbore. The downhole string of casing pipe is comprised of a plurality of pipe sections which are threadedly joined together. The pipe joints, also referred to as collars, have increased mass as compared to the pipe sections. After the strings of pipe have been cemented into the well, logging tools are run to determine the location of the casing collars. The logging tools used include a pipe joint locator whereby the depths of each of the pipe joints through which the logging tools are passed is recorded. The logging tools generally also include a gamma ray logging device which records the depths and the levels of naturally occurring gamma rays that are emitted from various well formations. The casing collar and gamma ray logs are correlated with previous open hole logs which results in a very accurate record of the depths of the pipe joints across the subterranean zones of interest and is typically referred to as the joint and tally log. After additional downhole completion hardware is installed, such as packers or screens, additional joint and tally logs may be run to locate these downhole elements for future reference.
Although modern oil and gas well production has progressed to a fine art, a variety of difficult problems may still be encountered during well completion, production, servicing and rework and it is often necessary to precisely locate one or more of the casing pipe joints or other downhole elements in a well. Of necessity, these situations must be remedied from the well platform for offshore wells or from the wellhead for land wells. Each well presents a unique challenge depending upon the well type, i.e., oil or gas, and the action to be taken. Typical problems requiring correction within a well are: crushed regions in the tubing, sand bridges or accumulation of paraffin, scale, rust or other debris. Maintenance procedures that must also be accomplished from the surface include, but are not limited to, the need to set or remove lock mandrels, bridge plugs, collar stops or safety valves. Specific, commercially-available tools have been developed for each of these maintenance actions or problem solutions.
To perform these remedial operations the well tool is deployed into the wellbore using a variety of methods. The tool may be deployed on wireline or tubing. The term tubing refers to either coiled or jointed tubing. The tool may, alternatively, be pumped down. The depth of a particular casing pipe joint adjacent or near the desired location at which the tool is to be positioned can readily be found on the previously recorded joint and tally log for the well.
Each of the deployment techniques mentioned require significant equipment and manpower to deploy the tool in the wellbore. In order to realize a significant cost saving in performing these remedial operations, a need exists for an autonomous system for performing the required well operations.